Magnetic material



May 15, 1928. 1,669,647

A. F. BANDUR MAGNETIC MATERIAL Filed April 17, 1926 //v z e/vfa/ Adm/[6404M Patented May 15, 1928.

Q5NITED STATES PATENT OFFICE.

ADOLPH rmmcrs BANDUR"; or BEBWYN, ILLINOIS, assrenon TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0! NEW YOB K, N. Y., A CORPORATION OF NEW YORK.

'IIAeNE'rIc MATERIAL.

Application flled' April 17, 1926. Serial No. 162,782.

This invention relates to magnetic mate rial and magnet cores, and more especially to magnet cores for loading coils for telephone circuits, and their method of production.

The principal object of the invention 1s the production of a magnetic element having low losses and a relatively high permeability to enable a given inductance to be obtained from a minimum amount of material and possessing to a high degree those electrical and magnetic characteristics which make 1t highlydesirable in electrical signallng apparatus, particularly in loading coils for telephone circuits.

In accordance with one embodiment, the present invention contemplates the construction of magnet cores of an alloy including nickel and iron in finely divided form combined with a suitable insulating material and heat treated to have a higher inherent mag netic permeability and lower inherent'hysteresis loss than iron. More specifically, the invention contemplates the formation of the magnet cores of a nickel iron alloy in finely divided form in which the proportions of its constituentsare more than 25% of nickel and the remainder principally iron, and in a form which has proven satisfactory the nickel content being approximately 78 92; of the whole. The metal particles are treated with a solution of a thick jelly-like hydrated alumina and a flux, such as boric acid, whereby the alloy particles are given a primary insulating coating after which the particles are dried and thoroughly mixed with kaolin until they have received a sec ondary insulating coating. The coated particles are then in a form to become pressed into cores of the desired shape and size. The cores so formed are finally heat treated to the optimum temperature for the particular alloy of which the cores are constructed to stabilize the insulator and to give a high permeability, low hysteresis losses and high specific resistance,-hence, low eddy current losses of the rings.

It is believed that the invention will be clearly understood from the following detailed description of one embodiment thereof and from the accompanying drawing, in which Fig. 1 is a perspective view of a section of a loading coil core made in accordance with the present invention, and

Fig. 2 shows a plurality of these sections assembled to form a completed core. It Wlll be understood, however, that this is merely illustrative and the invention is not limited to the production of this form of core but is adapted to the production of cores of magnetic particles of many forms. In carrying out the present invention. the magnetic material is prepared in the following manner: The magnetic material employed is preferably prepared from a nickel iron alloy commonly referred to as permalloy whlch is treated in a manner more fully described in the copending application of C.- P. Beath and H. M. E. Heinicke, Serial No. 101,179, filed April 10, 1926, to reduce the alloy to a finely divided form. Experience has proven that where low eddy current losses are desired it is essential that the particles be of small size and preferably of such size that all of the particles will readily pass through what is generally known as a 120 mesh screen and a large percentage pass through a 200 mesh screen. According to one embodiment of the invention, the alloy is prepared by melting approximately 78 parts of nickel and 21 parts of iron in an oxidizing atmosphere and pouring the resulting alloy into a mold. en prepared according to the foregoing process, the resulting alloy will be exceedingly brittle and is therefore particularly adapted to be reduced to a finely divided or dust form from which the finished cores are molded.

After the brittle ingots are obtained they the successively passed while hot through progressively reducing rolls which form the alloy into fiat slabs approximately onequarter of an inch thick. By the hot rolling process the size of the crystalline structure is materially reduced, which since the dis integration of the material takes place mainlyat the crystal boundaries, is essential in order to have the satisfactory yield of dust. The rolled slabs are broken into short pieces and are then crushed in a jaw crusher, hammer mill, or any other suitable type of apparatus in which a further reduction occurs. The material after being passed through the jaw crusher is subsequently rolled in a ball mill until it is reduced to a fine dust. The dust is sieved through a 120 mesh sieve and any residue is remelted and the foregoing operation is repeated to again reduce the' material to a finely divided form. Prior to the addition of the insulating material, the finely divided particles of the nickel iron alloy are annealed in a closed container at 5 a temperature of approximately 750 C. to 980 9., the temperature of about 925 C. having proven to be one which produces very satisfactory results. It is then necesmanner-:1 part of a thick, sticky mass 0 hydratedalumina is dissolved in 8 parts by weight of water and to this solution is addi of a flux, such as boric acid, equalto about 4% by weight of the hydratl. ed alumina. This solution 1 s thoroughly mixed and the permalloy particles added to thesolution, the amount of the permalloy particles added being determined by thepermeability desired and the particular use to which the finished cores are to be put. The

entire mass is then boiled to dryness accompanied by constant stirring-to prevent cake0 ing 'and to insure a thorough primary coat- 1 ing of the individual dust particles. After the drying is completed, the dry coated particles are placed in a revolving drum, and kaolin is added to give thepglirticles a secondary insulating coating, t e amount of kaolin used being determined by the characteristics desired in the finished core. This mixture is tumbled in the drum to thoroughmix the ingredients until the dust particles assume a uniform color which indicates that they are thoroughly coated with the secondary insulator. The insulated dust particles are then in a formsuitable for pressing into cores or rings which are preferablyformed with apressure of approximately 200,000 pounds per square inch. A high pressure is used in forming the rings in order to increasetheir density, since it has been found that the permeability of the rings increases with increased density. Finally the cores are transferred to an annealing furnace where they are annealed at a temperature of from 470 C. to 780 C. A few test rings may be made of dust insulate-d in the above manner and their permeability measured. Should their permeability be too low, it may be increased by the addition of a predetermined amount of uninsulated dust or dust which has a light coating of insulator, to the insulated dust before it is pressed into rings. A plurality of rings thus formed are stacked coaxially to form a core on which the usual toroidal winding is applied, the number of such rings used depending upon the existing electrical characteristics of the ed a quantity telephone circuit with which the loading coils are to be associated.

Although the permalloy particles have been described as being insulated by coating them with a solution of hydrated alumina and boric acid in definite proportions and by tumbling them with kaolin, it is, of course, to be understood that the proportions of the ingredients may be varied without departing from the spirit and scope of the invention. Also other fluxes, such as borax, common salt or magnesium sulphate may be used in place of the boric acid or sodium aluminate may be substituted for the hydrated alumina and flux, and the resulting cores in be satisfactory from both a magnetic and electrical standpoint.

By using an alloy of the proportions stated in the preceding paragraphs and by following the foregoing method of insulating the individual alloy particles and compressing the particles into cores or rings, magnet cores or rings are produced which'have extremely desirable electrical characteristics with a minimum amount of material employed. By the use of such cores or rings, inductance units having a higher permeability with equal or less hysteresis and eddy current losses as cores constructed according to previously known methods, but with much less core volume and much less coil volume, are available.

What is claimed is:

1. As a new article of manufacture, a magnetic substance composediof particles of a magnetic material, and a plurality of coatings of different insulating materials applied in successive layers on the particles.

2. As a new article of manufacture, a magnetic substance composed of particles of a magnetic material, a primary insulating coating .of hydrated alumina and boric acid, and a secondary insulating coating of kaolin separating the particles.

3. As a new article of manufacture, a magnetic substance composed of finely divided particles of a nickel iron alloy, a primary insulating coating consisting of 1 part hydrated alumina and 4/100 parts boric acid. and a secondary insulating coating of kaolin separating the particles.

4. As a new article of manufacture, a magnetic substance composed of particles of a magnetic material, and an insulating coating consisting of hydrated alumina, boric acid, and kaolin.

5. As a new article of manufacture, a magnetic substance composed of a ma etic alloy of nickel and iron, and an insu ting material consisting of hydrated alumina, boric acid, and kaolin. a

6. As a new article of manufacture, a magnetic substance composed of finely divided particles of a magnetic alloy composed of more than 25% nickel and the remainder principally iron, and an insulat material posed of more than 25% nickel and the reinsulated particles into ducing theproduct so 0 a homogeneous solid.

' sists in reducing the alloy particles,

mainder principally iron, and an insulating material consisti of 1 part b drated alumina, 4/100 parts ric acid, an kaolin.

8. The method of making magnetic structures, which consists in coating particles of a magnetic material with an insulating ma terial, consisting of h drated alumina, boric acid and kaolin, and orming a mass of such a homogenous solid.

9. The method of making magnetic structures, which consists in coating particles of i an alloy composed of more than 25% nickel and the remainder principally iron with an insulating material consisting of hydrated alumina, boric acid and kaohn.

' 10. The method of making magnetic structures composed of an allo which conto finely divided articles, a in retained to ely divided particles, coating the particles with an insulating material comprising h drated alumina, boric acid and kaolin, and formmg a mass of such insulated particles into particles, heating the 11. The method of making magnetic structures composed of an alloy of nickel and iron which consists in reducing the'alby to finely divided particles, heating the again reducing the roductso obtained to finely divided particliis, coating the particles with an insulating materialcomprising hydrated al a, boric acid and kaolin, forming a mass of such insulated particles into a homogeneous solid, and heating the solid mass to a high temperature.

12. The method of making magnetic structures composed of an alloy of more than 25% nickel and the remainder rincipally iron, which consists in reducing t e alloy to finely divided particles, heating the particles, a ain reducing the product soobtained to fine y divided particles, coatin the particles with an insulating materia comprising hydrated alumina, boric acid and kaolin,

forminga mass of such insulated particles Into a homogeneous solid, and heating the solid mass to a high temperature.

13. The method of making magnetic .structures, which consists in envelopin particles of a magnetic material with a p urality of coatings of an insulating material in successive layers, forming a mass of such insulated particles into a homogeneous solid, and-heat treating the solid at a high temperature. Y

14. The method of making magnetic structures, which consists in enveloping particles of a magnetic material with a primary coating of an insulator of one composition, enveloping the coated particles with a secondary coating of an insulator of another composition, and forming a mass of such in-.

sulated particles into a homogeneous solid. 15. The method of making magnetic structures, which consists in enveloping finely divided-particles of a nickel iron alloy with a primary coating ofan insulating material, consisting of hydrated alumina and 'boric acid, enveloping the coated particles with a secondary insulatin coating of kaolin,.and forming a mass 0 such insulated articles into a homo eneous solid.

16. he method of ma ing magnetic structures, which consists in enveloping finely divided particles of a magnetic alloy comprising more than 25% nickel and the remainder principally iron with a primary coating 0 an insulating material consisting of 1 part hydrated alumina and 4/100 parts boric acid, enveloping the coated particles with a secondary insulating coatin of kaolin, forming a mass of such insulate particles into a homogeneous solid, and heat- 

